Once I noticed that new servers running Ubuntu Server 18.04 operating systems periodically send email notifications:
Cron <email@example.com> test -x /usr/sbin/anacron || ( cd / && run-parts –report /etc/cron.weekly )
New release ‘20.04.1 LTS’ available.
Run ‘do-release-upgrade’ to upgrade to it.
As it turned out, this is executed by the /etc/update-motd.d/91-release-upgrade script.
To disable notifications, open the /etc/update-manager/release-upgrades file in a text editor, find the line:
And change to:
Or you can quickly change it with the command below:
sed -i 's/^Prompt.*/Prompt=never/' /etc/update-manager/release-upgrades
See also my article:
How to disable auto-update on Ubuntu 18